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e-Electric General Discussion > Stepdown diode question
 
 
krashtagain
Key Veteran
Location: ohio

My Posts This: Topic  Forum		Does anyone know which diode is needed to make a stepdown from 7.4v to 5.1v ?

If you're not living on the edge you're just taking up space !
05-19-2009 03:02 AM
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DKNguyen
Senior Heliman
Location: Alberta, Canada

My Posts This: Topic  Forum		How much current? Each TYPICAL diode will drop about 0.7V. (Not ultra fast, schottky, or anything fancy like that).
05-19-2009 05:12 AM
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Quandumphone
Senior Heliman
Location: Yuma, AZ

My Posts This: Topic  Forum		It would take about three or four of them inline to do it but if you need to go that far, you should use a 6 volt regulator. Stacking diodes like that would be an ugly solution on several levels.

That 7.4 volts I'm guessing is from a lipo, which will really start out about 8.2 volts and will throw off the calculation for the diodes. You will either be too high or too low and only pass through the correct voltage momentarily.

A regulator will give you a constant voltage, 6 volts in this case, and you would need one diode for the tail servo. All devices would see a constant voltage, which is desirable.
05-19-2009 06:03 AM
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krashtagain
Key Veteran
Location: ohio

My Posts This: Topic  Forum		That was my intent of this thread was to build a stepdown for the tail servo . Maybe I should have said that from the beginning. So I would only need 1 diode inline for the tail servo ?

If you're not living on the edge you're just taking up space !
05-19-2009 11:05 AM
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Quandumphone
Senior Heliman
Location: Yuma, AZ

My Posts This: Topic  Forum		No, I'm saying you should use a regulator. You can use a 6 volt regulator with one diode or a 5 volt regulator with no diode. Trying to step down from a lipo with only diodes at 8.2 starting volts is asking for trouble. Use a regulator, there's several out there that are reasonably priced and probably the same price as buying a bunch of diodes.
05-19-2009 05:25 PM
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krashtagain
Key Veteran
Location: ohio

My Posts This: Topic  Forum		I'm using a bec. I just wanted to make a stepdown for the tail instead of hitting the tail servo with 6 volts.

If you're not living on the edge you're just taking up space !
05-19-2009 05:57 PM
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Zaneman007
Elite Veteran
Location: Texas - USA

My Posts This: Topic  Forum		You do not want to use diodes if the input voltage is unregulated.

JR or is it Spectrum that makes a step down "regulator" for the tail servo for guys using unregulated voltage on the servos. There are also other options for stepping down the voltage to the tail servo with an unregulated 7.4 volt system. (AR7100, Kiwi(arizona reg)). But not one or more diodes.

Old Guys Rule!
05-19-2009 06:19 PM
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Quandumphone
Senior Heliman
Location: Yuma, AZ

My Posts This: Topic  Forum		If it's 6 volts, then use one diode.
05-19-2009 06:23 PM
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Gyronut
Elite Veteran
Location: Martinsville In.

My Posts This: Topic  Forum		a 1N4007 diode will get the job done.

Rick
05-19-2009 06:51 PM
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DarkSide41
Senior Heliman
Location: Sylacauga Alabama USA

My Posts This: Topic  Forum		+ 1 , that's all I use .
http://www.radioshack.com/product/i...oductId=2062589

What goes up....ALWAYS comes down .
05-22-2009 11:32 AM
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BEEP BEEP
Senior Heliman
Location: Alexandria, La.

My Posts This: Topic  Forum		Hi,Everyone
Can the diode be mounted in the servos lead (wire). Anyone have pics.
Thanks,Gator
06-20-2009 10:19 PM
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Bruce Naylor
Senior Heliman
Location: Swindon, Wiltshire, UK

My Posts This: Topic  Forum		So you're stepping down your 6v to 5.3v with a diode to drive the servo. What about the signal. Are all servos happy running at 5.3v with a square wave hitting it at 6v?

Would it not be prudent to also put a 1N4001 in the signal wire?

Just a thought?

B.

"If you know what you're doing, you're not learning much"
11-04-2009 02:03 PM
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Climax
Veteran
Location: West London, United Kingdom

My Posts This: Topic  Forum		This is unlikely to be a problem...

Most receivers have a fairly modest output voltage with regard to the PWM servo signal.

Typically these signals come straight out of a micro-controller that itself is running from an internally (i.e. within the RX) regulated power supply. Don't get confused by the concept of an internal regulator, this is purely for the RX's processor and other internal electronics - it has nothing to do with powering servos.

An increasing number of receivers now use 3.3 volt internals and thus the servos drive signal will be slightly lower still.

Many receivers also feature line termination resistors in series with the servo drive signals, these will also limit current if required.

Don't know if any of this helps?
11-04-2009 02:18 PM
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Bruce Naylor
Senior Heliman
Location: Swindon, Wiltshire, UK

My Posts This: Topic  Forum		Yes, assumed that Vin = Vout. Makes sense that modern processor controled rx's would be regulated below the nominal 4.8v rx battery, and hense the signal would be lower.

I should have dusted down the 'scope and taken a closer look first.

Bruce.

"If you know what you're doing, you're not learning much"
11-04-2009 02:50 PM
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e-Electric General Discussion > Stepdown diode question
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